1. Field of the Invention
The present invention relates to image display apparatus and, for example, is suitably applicable to head mounted displays (HMDs), goggle type displays, and so on using a reflection type liquid crystal display element as a display element for displaying image information for observation and permitting an observer to observe an enlarged image of the image information displayed on the display element, through an optical element appropriately set.
2. Related Background Art
A variety of proposals have been made heretofore on head-worn image observation apparatus (image display apparatus), so called head mounted displays (HMDs), for presenting an enlarged virtual image of image information displayed on an image display element such as a liquid crystal display or the like.
Among these, the HMDs using the reflective display element were proposed, for example, in Japanese Patent Application Laid-Open Nos. 7-128614, 11-125791, 11-337863, 2000-10041, and so on.
The HMDs proposed in these applications are those constructed in such structure that light emitted from an illumination light source is reflected on a reflective liquid crystal display and that the reflected light is guided to the eye to permit observation of an enlarged image of the image displayed on the liquid crystal display. In this structure the light travels from the illumination light source via an illumination optical system, the reflective liquid crystal display, and a display optical system to the eye in the order named. In a disclosed embodiment of the HMD proposed in the Japanese Patent Application Laid-Open No. 11-125791, the light from the illumination light source directly illuminates the reflective liquid crystal display without use of the illumination optical system. In this case there is also an example in which no shared surface exists between the illumination optical system and the display optical system. In this structure, in order to prevent the light from the illumination light source from being eclipsed, a large space is necessary between the illumination light source and the reflective liquid crystal display, so that the apparatus tends to become large in size. In most of the embodiments proposed in the other applications, there exists a shared surface or shared surfaces between the illumination optical system and the display optical system. With existence of the shared surface(s), the optical paths of the illumination optical system and the display optical system overlap with each other and this facilitates reduction of size. However, as the number of such common surfaces increases, the optical systems become more complex and loss of light amount also increases. Meanwhile, the inventor proposed a compact display optical system for HMD in Japanese Patent Application Laid-Open No. 7-333551. This application describes the reduction of size of the entire apparatus by use of a free-form surface prism. Further, the inventor also proposed the HMDs including combination of the free-form surface prism with the reflective display element in Japanese Patent Application Laid-Open Nos. 11-125791, 11-337863, and 2000-10041.
In the field of the image observation apparatus such as the HMDs and the like, an important subject has been and is to reduce the size and weight of the entire apparatus, because the apparatus is mounted on the observer's head. In addition, another important subject is to permit the observer to well observe the image information displayed on the display means.
When the reflective liquid crystal display element is used as an image display device, the illumination device for illuminating it needs to be appropriately built in the apparatus, in order to decrease the size of the entire apparatus.
For example, when the apparatus is constructed in such structure that for illuminating the reflective liquid crystal display with the light from the illumination light source, the light travels via a lot of reflective and transmissive surfaces or travels through a prism body of long optical path lengths, there inevitably occurs loss in the amount of the light from the illumination light source before arrival at the reflective liquid crystal display. Therefore, there are desires for HMDs having the display optical system and the illumination optical system both being compact and causing little loss of light amount.
An object of the present invention is to provide image observation apparatus for permitting an observer to observe image information displayed on a display means such as a liquid crystal display or the like, which realizes reduced loss of light amount while accomplishing the reduction of size of the entire apparatus and which permits the observer to observe the image information with good image quality, by properly setting configurations of the illumination optical system from the light source means to the display means and the display optical system for guiding the light from the display means to the observer's eye, and also provide head mounted displays using it.